Method of fabricating ultra-deep vias and three-dimensional integrated circuits using ultra-deep vias

ABSTRACT

A method of forming a high aspect ratio via opening through multiple dielectric layers, a high aspect ratio electrically conductive via, methods of forming three-dimension integrated circuits, and three-dimensional integrated circuits. The methods include forming a stack of at least four dielectric layers and etching the first and third dielectric layers with processes selective to the second and fourth dielectric layers, etching the second and third dielectric layers with processes selective to the first and second dielectric layers. Advantageously the process used to etch the third dielectric layer is not substantially selective to the first dielectric layer.

RELATED APPLICATIONS

This Application is related to application Ser. No. ______ filed on______.

FIELD OF THE INVENTION

The present invention relates to the field of integrated circuits; morespecifically, it relates to structures of and methods for fabricatingultra-deep vias in integrated circuits and structures of and methods forfabricating three-dimensional integrated circuits.

BACKGROUND OF THE INVENTION

In order to reduce the footprint and improve the speed of integratedcircuits various three-dimensional integrated circuit structures havebeen proposed. Traditional integrated circuit structures have been twodimensional, in that all the active devices have been formed in a sameplane in a same semiconductor layer. Three-dimensional integratedcircuits utilize vertically stacked semiconductor layers with activedevices formed in each of the stacked semiconductor layers.

The fabrication of three-dimensional integrated circuits poses manychallenges particularly in the methodology for interconnecting devicesin the different semiconductor layers together. The total depth of theseinterconnects can exceed 1.5 um with diameters in the sub 0.2 um range.It is difficult to fill vias having such large depth to width aspectratios with high quality, defect free metal. In particular, the metalfill of large aspect ratio and very deep vias often contain voids whichcan increase the resistance of the via and result in yield loss as wellas reduce the reliability of the device. Accordingly, there exists aneed in the art to overcome the deficiencies and limitations describedhereinabove.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a method, comprising: formingan etch stop layer on a top surface of a substrate; forming a firstdielectric layer on a top surface of the etch stop layer; forming aprofile modulation layer on a top surface of the first dielectric layer;forming a second dielectric layer on a top surface of the profilemodulation layer; forming a photo-imaging layer on a top surface of thesecond dielectric layer; forming an opening in the photo-imaging layer,a region of the top surface of the second dielectric layer exposed in abottom of the opening; reactive ion etching the second dielectric layerwith a first etch chemistry selective to the profile modulation layer toform an opening through the second dielectric layer; reactive ionetching the profile modulation layer with a second etch chemistryselective to the first and second dielectric layers to extend theopening through the profile modulation layer; reactive ion etching thefirst dielectric layer with a third etch chemistry selective to theprofile modulation layer and selective to the etch stop layer to extendthe opening through the first dielectric layer; reactive ion etching theetch stop layer with a fourth etch chemistry selective to the first andsecond dielectric layers to extend the opening through the etch stoplayer; and removing the photo-imaging layer, after the removing thephoto-imaging layer, the opening extending from the top surface of thesecond dielectric layer, through the second dielectric layer, throughthe profile modulation layer, through the first dielectric layer andthrough the etch stop layer to the top surface of the substrate.

A second aspect of the present invention is the first aspect, whereinthe third etch chemistry is not selective to the second dielectriclayer.

A third aspect of the present invention is the first aspect, wherein thefirst and third etch chemistries are a same chemistry.

A fourth aspect of the present invention is the first aspect, whereinthe second and fourth etch chemistries are a same chemistry.

A fifth aspect of the present invention is the first aspect, wherein theremoving the photo-imaging layer is performed between the reactive ionetching the first dielectric layer and the reactive ion etching the etchstop layer.

A sixth aspect of the present invention is the first aspect, wherein thefirst dielectric layer and second dielectric layer comprise siliconoxide and the profile modulation layer and the etch stop layer comprisesilicon nitride.

A seventh aspect of the present invention is the first aspect, wherein:a first width of the opening measured in first direction parallel to thetop surface of the second dielectric layer at the top surface of thesecond dielectric layer is greater than a second width of the openingmeasured in the first direction at the top surface of the profilemodulation layer and greater than a third width of the opening measuredin the first direction at the top surface of the substrate, the secondwidth greater than or equal to the third width; and wherein a ratio of adepth of the opening measured in a second direction perpendicular to thefirst direction from the top surface of the second dielectric layer tothe top surface of the substrate to the first width is equal to orgreater than five.

An eighth second aspect of the present invention is the first aspect,further including: after the removing the photo-imaging layer, fillingthe opening with the electrical conductor.

A ninth aspect of the present invention is the eighth aspect, whereinthe filling the opening with an electrical conductor comprises:depositing a tantalum nitride layer over sidewalls and a bottom of theopening; depositing a tantalum layer on the tantalum nitride layer;depositing a seed copper layer the tantalum layer; electroplating anelectroplated copper layer on the seed copper layer, the electroplatedcopper layer completely filling remaining spaces in the opening; andperforming a chemical-mechanical-polish to remove the tantalum nitridelayer, the tantalum layer, the seed copper layer and the electroplatedcopper layer from over the top surface of the second dielectric layer.

A tenth aspect of the present invention is the first aspect, wherein thephoto-imaging layer includes a photoresist layer over an antireflectivecoating on the top surface of the first dielectric layer and the formingthe opening in the photo-imaging layer comprises exposing thephotoresist layer to actinic radiation through a patterned photomask,developing the exposed photoresist layer and reactive ion etching theantireflective coating with an initial etch chemistry where theanti-reflective coating is not protected by the photoresist layer.

An eleventh second aspect of the present invention is the tenth aspect,wherein the initial etch chemistry is selective to the photoresist layerand the first dielectric layer and wherein the initial, second andfourth etch chemistries are a same chemistry.

A twelfth aspect of the present invention is a structure comprising:forming a first substrate, the first substrate including: firsttransistors electrically connected to a set of wiring levels, eachwiring level including electrically conductive wires in a respectivedielectric layer; an etch stop layer on a top surface of an uppermostwiring level of the set of wiring levels that is furthest from thesubstrate, the etch stop layer in contact with a wire of the uppermostwiring level; and a first dielectric bonding layer on a top surface ofthe etch stop layer; forming a second substrate, the second substrateincluding: a second dielectric bonding layer; a buried oxide layer on atop surface of the second dielectric bonding layer; a semiconductorlayer on a top surface of the buried oxide layer, the semiconductorlayer including second transistors electrically isolated from each otherby dielectric isolation in the silicon layer; a profile modulation layeron a top of the silicon layer and on a top surface of the dielectricisolation; and a first dielectric layer on a top surface of the profilemodulation layer; bonding a top surface of the first dielectric bondinglayer to a bottom surface of the second dielectric bonding layer, thefirst and second dielectric bonding layers, the buried oxide layer andthe dielectric isolation comprising a multilayer second dielectriclayer; forming a photo-imaging layer on a top surface of the firstdielectric layer; forming an opening in the photo-imaging layer, aregion of the top surface of the first dielectric layer exposed in abottom of the opening; reactive ion etching the first dielectric layerwith a first etch chemistry selective to the profile modulation layer toform an opening through the first dielectric layer; reactive ion etchingthe profile modulation layer with a second etch chemistry selective tothe first and second dielectric layers to extend the opening through theprofile modulation layer; reactive ion etching the second dielectriclayer with a third etch chemistry selective to the profile modulationlayer and selective to the etch stop layer to extend the opening throughthe second dielectric layer; reactive ion etching the etch stop layerwith a fourth etch chemistry selective to the first and seconddielectric layers and to the wire to extend the opening through the etchstop layer; removing the photo-imaging layer, after the removing thephoto-imaging layer the opening extending from the top surface of thefirst dielectric layer, through the profile modulation layer, throughthe second dielectric layer, through the second dielectric layer andthrough the etch stop layer to a top surface of the wire; and fillingthe opening with an electrical conductor, the electrical conductor inelectrical contact with the wire.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention are set forth in the appended claims. Theinvention itself, however, will be best understood by reference to thefollowing detailed description of an illustrative embodiment when readin conjunction with the accompanying drawings, wherein:

FIGS. 1A through 1J are cross-sections of the fabrication of anexemplary electrically conductive via according to embodiments of thepresent invention;

FIGS. 2A through 2C are cross-sections of the fabrication of a firstexemplary three dimensional integrated circuit according to embodimentsof the present invention; and

FIG. 3 is a cross-section of additional fabrication steps in thefabrication of three-dimensional integrated circuit according toembodiments of the present.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A through 1J are cross-sections of the fabrication of anexemplary electrically conductive via according to embodiments of thepresent invention. In FIG. 1A, formed in a semiconductor substrate 100is a metal wire 105. Formed on a top surface 110 of substrate 100 is adielectric etch stop layer 115. Formed on top of etch stop layer 115 isa first dielectric layer 120. Formed on first dielectric layer 120 is asecond dielectric layer 125. Formed on second dielectric layer 125 is athird dielectric layer 130. Formed on top of third dielectric layer 130is a profile modulation layer 135. Formed on profile modulation layer135 is a fourth dielectric layer 140. Semiconductor substrate 100 maycomprise, for example, Si, SiGe, Ge, GaAs or InP.

The stack of dielectric materials consisting of dielectric etch stoplayer 115, first dielectric layer 120, second dielectric layer 125,third dielectric layer 130, profile modulation layer 135 and fourthdielectric layer 140 simulates a structure that conductive vias areformed through in fabrication of a three-dimensional integrated circuitaccording to embodiments of the present invention described infra.Therefore in one example, etch stop layer 115 and first dielectric layer120 represent layers on a lower semiconductor substrate and seconddielectric layer 125, third dielectric layer 130, profile modulationlayer 135 and fourth dielectric layer 140 represent layers on an uppersemiconductor layers with first and second dielectric layers 120 and 125representing oxide bonding layers that bond the two substrates together.Third dielectric layer 130 represents a dielectric trench isolation (TI)or dielectric shallow trench isolation (STI) on a buried oxide layer(BOX) of a silicon-on-insulator (SOI) substrate.

In accordance with the simulation of a three-dimensional integratedcircuit according to embodiments of the present invention, etch stoplayer 115 is silicon nitride and in one example is about 500 Å thick,first dielectric layer 120 is low temperature silicon oxide (LTO) and inone example is between about 2500 Å and about 3500 Å thick, seconddielectric layer 125 is LTO and in one example is between about 2500 Åand about 3500 Å thick, third dielectric layer 130 is high densityplasma silicon (HDP) oxide thermal oxide and in one example is about3600 Å thick, profile modulation layer 135 is silicon nitride and in oneexample is about 500 Å thick and fourth dielectric layer 140 is HDPoxide and in one example is about 4700 Å thick. In one example, metalwire 105 comprises copper. The HDP oxide of third dielectric layer 130and fourth dielectric layer 140 may be independently replaced withplasma enhanced chemical vapor deposition (PECVD) oxide, ultrahighdensity plasma (UHP) oxide, tetraethoxysilane (TEOS) oxide orspin-on-oxide. The silicon nitride of etch stop layer 115 and profilemodulation layer 135 may be independently replaced with silicon carbide,silicon oxy nitride, silicon oxy carbide or Nblock (SiCNH). In oxidefusion bonding applications, first and second dielectric layer are LTO,but in other application may be independently thermal oxide, HDP oxide,PECVD oxide, UDP oxide, TEOS oxide or spin-on-oxide. In one example,thicknesses of etch stop layer 115 and profile modulation layer 135 areindependently about 5 times less than a thickness of either fourthdielectric layer 140 or a combined thickness of first, second and thirddielectric layers 120, 125 and 130.

An LTO oxide is a silicon oxide that is formed at temperatures belowabout 350° C. In one example, LTO oxides are formed using N₂O in aplasma enhanced chemical vapor deposition (PECVD) process. An HDP oxideare specifically prepared to be fusion bonded to each other.

First second, third and fourth dielectric layers 120, 125, 130 and 140are advantageously first similar materials (e.g., silicon oxides) andetch stop layer 115 and profile modulation layer 135 are advantageouslysecond similar materials (e.g. silicon nitrides), where the secondmaterials may be selectively plasma etched relative to the firstmaterials.

In FIG. 1B, an optional antireflective coating (ARC) 145 is formed onfourth dielectric layer and a photoresist layer 150 formed on top of theARC. An opening 155 is formed in photoresist layer 150photolithographically by exposing photoresist layer 150 to actinicradiation through a patterned photomask and then developing thephotoresist layer to transfer the pattern of the photomask into thephotoresist layer. A region of ARC 145 is exposed in the bottom ofopening 155. ARC 145 is a bottom ARC or BARC since it is formed underphotoresist layer 150. A top ARC (TARC) formed over the photoresist maybe substituted or both a TARC and BARC may be used. The combination of aphotoresist layer and an ARC (i.e., BARC, TARC or both BARC and TARC) isdefined as a photo-imaging layer.

In FIG. 1C, the region of ARC 145 exposed in opening 155 of FIG. 1B isremoved using a reactive ion etch (RIE) that etches ARC 145 faster thanphotoresist layer 150 (i.e., ARC 145 is RIE'd selective to photoresistlayer 150) to expose a region of fourth dielectric layer 140 in thebottom of an opening 155A. An example RIE process for etching ARC 145includes etching with a mixed CF₄/CHF₃/Ar/O₂ gas derived plasma.

In FIG. 1D, the region of fourth dielectric layer 140 exposed in opening155A of FIG. 1C is removed using an RIE that etches fourth dielectriclayer 140 faster than profile modulation layer 135 (i.e., fourthdielectric layer 140 is RIE'd selective to profile modulation layer 135)to expose a region of the profile modulation layer in the bottom of anopening 155B. Note, photoresist layer 150 and ARC 145 are eroded by thefourth dielectric layer 140 RIE etch. The opening in the top surface ofphotoresist layer 150 is larger than the opening in the bottom surfaceof the photoresist layer. An example RIE process for etching fourthdielectric layer includes etching with a mixed CO/C₄F₈/Ar gas derivedplasma. This chemistry (at the proper bias, forward and reverse power,pressure and gas flows) etches silicon oxide about 25 times faster thansilicon nitride.

In FIG. 1E, the region of profile modulation layer 135 exposed inopening 155B of FIG. 1D is removed using an RIE that etches profilemodulation layer 135 faster than third dielectric layer 130 (i.e.,profile modulation layer 135 is RIE'd selective to third dielectriclayer 130) to expose a region of the third dielectric layer in thebottom of an opening 155C. An example RIE process for etching profilemodulation layer includes etching with a mixed CHF₃/CF₄/Ar gas derivedplasma. This chemistry (at the proper bias, forward and reverse power,pressure and gas flows) etches silicon nitride about 4 times faster thansilicon oxide. It is advantageous to keep profile modulation layer 135(and etch stop layer 115) as thin as possible.

In FIG. 1F, the region of third dielectric layer 130 exposed in opening155C of FIG. 1E is removed along with regions of second and firstdielectric layers 125 and 120 aligned under opening 155C of FIG. 1Eusing an RIE that etches third, second and first dielectric layers 130,125 and 120 faster than etch stop layer 115 and profile modulation layer135 (i.e., third dielectric layer 130 is RIE'd selective to etch stoplayer 115 and profile modulation layer 135) to expose a region of theetch stop layer in the bottom of an opening 155D. An example RIE processfor etching third, second and first dielectric layers 130, 125 and 120includes etching with a mixed CO/C₄F₈/Ar gas derived plasma. Note,photoresist layer 150 and ARC 145 are further eroded by the thirddielectric layer 130, second dielectric layer 125 and first dielectric120 RIE etches. This etch is not selective to fourth dielectric layer140 and in combination with the further erosion of photoresist layer 150and ARC 145, a tapered upper region 160 of opening 155D is formed in theregion of opening 155D formed through fourth dielectric layer 140. Thesidewall of opening 155D in region 160 taper at an angle “a” measuredbetween the sidewall and a plane parallel to top surface 110 ofsubstrate 100. A lower region 165 of opening 155D is formed throughprofile modulation layer 135 and third, second and first dielectriclayers 130, 125 and 120. The sidewall of opening 155D in region 165 isat an angle “b” measured between the sidewall and a plane parallel totop surface 110 of substrate 100. Opening 155D has width W1 measured atthe top surface of fourth dielectric layer 140, a width W2 measured at atop surface of profile modulation layer 135 and a width W3, measured ata top surface of etch stop layer 115. W1 is greater than W2. In oneexample W1 is about 0.28 microns and W3 is about 0.16 microns.

In one example, W2 is equal to W3 and angle “b” is between about 87° andno greater than 90°. In one example W2 is greater than W3, however angle“b” is less than angle “a.” Again, the presence of profile modulationlayer 135 allows the widening of opening 155D at the top surface offourth dielectric layer 140 in upper region 160 due to the controllederosion of photoresist layer 150 while facilitating formation of astraight or sidewall in lower region 165. Without profile modulationlayer 135, either opening 155D would be to narrow at the top to befilled with metal without incorporating large voids in the metal fill,or the value of W1 would need to be much greater to maintain the samevalue of W3 obtained with the presence of the profile modulation layer.

In FIG. 1G, photoresist layer 150 and arc 145 (See FIG. 1F) are removedusing an oxygen ash process (i.e., O₂ plasma etch). Alternatively, thisstep may be performed after the process illustrated in FIG. 1H. It isadvantageous to perform the photoresist removal step with etch stoplayer 115 intact to prevent the photoresist removal process fromoxidizing wire 105 particularly when wire 105 comprises copper.

In FIG. 1H, the region of etch stop layer 115 exposed in opening 155D ofFIG. 1G is removed using an RIE that etches stop layer 115 faster thanfirst, second, third dielectric layers 120, 125 and 130 (i.e., etch stoplayer 115 is RIE'd selective to first, second and third dielectriclayers 120, 125 and 130, metal wire 105 and optionally fourth dielectriclayer 140) to expose a region of metal wire 105 in the bottom of anopening 155E. An example RIE process for etching etch stop layer 115includes etching with a mixed CF₄/CHF₃/Ar/O₂ gas derived plasma. Region160 has a height H1 measured from the top surface of fourth dielectriclayer 140 to the top surface of profile modulation layer 135 in adirection perpendicular to the top surface of wire 105 in substrate 100.Region 165 has a height H2 measured from the top surface of profilemodulation layer 134 to the top surface of wire 105 in substrate 100 ina direction perpendicular to the top surface of wire 105 in substrate100. In one example H1 is about 0.4 microns and H2 is between about 1micron an and about 1.6 microns for total opening depth (i.e., H1+H2) ofbetween about 1.4 microns and about 2.0 microns. With a value of W3 (seeFIG. 1F) of about 0.16 microns the depth to width ratio of opening 155Eis between about 1.4/0.16 about 8.75 and about 2.0/0.16=about 12.5. Inone example, H1+H2 is equal to or greater than about 1 micron. In oneexample, H1+H2 is equal to or greater than about 2 microns. In oneexample (H1+H2)/W1 is greater than or equal to 5. In one example(H1+H2)/W1 is greater than or equal to 8.

In FIG. 1I, an optional direct current (DC) clean (e.g., sputtercleaning with an inert gas) is performed followed by formation of anelectrically conductive liner 170 on the sidewall of opening 155E andtop surface of fourth dielectric layer 140 followed by overfilling theopening 155E with an electrically conductive core conductor 175. In oneexample, conductive liner 170 comprises, in the order of deposition, alayer of TaN, a layer of Ta and a layer of Cu and core conductor 175comprises electroplated copper.

In FIG. 1J, a chemical-mechanical-polish (CMP) is performed to removeliner 170 and core conductor 175 from over fourth dielectric layer 140to form an electrically conductive via 180 extending from a top surface185 of the fourth dielectric layer to a top surface of wire 105 (makingelectrical contact with wire 105). After the CMP, a top surface 190 ofvia 180 is coplanar with top surface 185 of fourth dielectric layer 140.

It should be understood in the simplest form, embodiments of the presentinvention may be practiced on a dielectric stack where first, second andthird dielectric layers 120, 125 and 130 of FIG. 1 are replaced with asingle dielectric layer. In other embodiments, their may be more thanthree dielectric layers in the stack represented by first, second andthird dielectric layers 120, 125 and 130 of FIG. 1, though they shouldall be similar materials (e.g., silicon oxides) or have similarselectivity's to the RIE used to etch stop and profile modulationlayers.

FIGS. 2A through 2C are cross-sections of the fabrication of a firstexemplary three-dimensional integrated circuit according to embodimentsof the present invention. In FIG. 2A, an upper semiconductor substrate200 includes a silicon oxide bonding layer 205, a BOX layer 210 on thebonding layer, a semiconductor layer 215 including semiconductor regions220 and STI 225 formed in the semiconductor layer, a profile modulationlayer 230 on top of semiconductor layer 215 and a dielectric layer 235on the passivation layer. Exemplary, field effect transistors (FETs) 240comprising source/drains (S/D) formed in semiconductor regions 220 andgates formed over the silicon regions between the S/Ds are formed insubstrate 200. Semiconductor layer 215 may comprise, for example, Si,SiGe, Ge, GaAs or InP.

Etch stop layer may also serve as a diffusion barrier layer for copperand/or as a passivation layer.

A substrate 300 includes a semiconductor base later 305, a BOX layer 310on the base silicon layer, a semiconductor layer 315 includingsemiconductor regions 320 and STI 325 formed in the silicon layer, aninterlevel dielectric (ILD) wiring set 330 including contacts 335 andwires 340 and 350 formed in respective dielectric layers of dielectriclayers 355 of ILD wiring set 330. Semiconductor base layer 305 maycomprise, for example, Si, SiGe, Ge, GaAs or InP. Semiconductor layer315 may comprise, for example, Si, SiGe, Ge, GaAs or InP.

An ILD wiring level comprises a dielectric layer and one or more wires,vias or contacts embedded therein. ILD wiring set 330 is illustratedhaving three ILD wiring levels. ILD wiring set 330 may include more orless ILD levels (down to one level containing contacts 335) or as manylevels as required by the integrated circuit design. The ILD wiringlevels of ILD wiring set 330 are, by way of example, damascene anddual-damascene ILD levels formed by damascene and dual-damasceneprocesses.

A damascene process is one in which wire trenches or via openings areformed in a dielectric layer, an electrical conductor of sufficientthickness to fill the trenches is deposited on a top surface of thedielectric, and a chemical-mechanical-polish (CMP) process is performedto remove excess conductor and make the surface of the conductorco-planar with the surface of the dielectric layer to form damascenewires (or damascene vias). When only a trench and a wire (or a viaopening and a via) is formed the process is called single-damascene.

A dual-damascene process is one in which via openings are formed throughthe entire thickness of a dielectric layer followed by formation oftrenches part of the way through the dielectric layer in any givencross-sectional view. All via openings are intersected by integral wiretrenches above and by a wire trench below, but not all trenches needintersect a via opening. An electrical conductor of sufficient thicknessto fill the trenches and via opening is deposited on a top surface ofthe dielectric and a CMP process is performed to make the surface of theconductor in the trench co-planar with the surface the dielectric layerto form dual-damascene wires and dual-damascene wires having integraldual-damascene vias.

Returning to FIG. 2A, exemplary, field effect transistors (FETs) 345comprising source/drains (S/D) formed in semiconductor regions 320 andgates formed over the silicon regions between the S/Ds are formed insubstrate 300. Contacts 335 and wires 340 electrically connect FETs 345into circuits or portions of circuits. Substrate 300 further includes anetch stop layer 360 on top of ILD wiring set 355 and a silicon oxidebonding layer 365 on the etch stop layer. Bonding layers 205 and 365bond substrates 200 and 300 into a single structure. The bonding processincludes placing the bonding layers 205 and 365 in contact at atemperature above room temperature but below, for example, 350° C.

In one example, dielectric layers 235, 355 and STI 225 are independentlyselected from the group consisting of thermal oxide, HDP oxide, PECVDoxide, UDP oxide, TEOS oxide and spin-on-oxide, and bonding layers 205and 365 are LTO. In one example profile modulation layer 230 and etchstop layer 360 are independently selected from the group consisting ofsilicon nitride, silicon carbide, silicon oxy nitride or silicon oxycarbide. In a second example, dielectric layers 235, 355 and STI 225 andbonding layers 205 and 365 are advantageously first similar materials(e.g., silicon oxides) and etch stop layer 360 and profile modulationlayer 230 are advantageously second similar materials (e.g. siliconnitrides), where the first and second materials may be selectivelyplasma etched relative to each other. In one example, dielectric layer235 is between about 2500 Å and about 7500 Å thick. In one example,profile modulation layer 230 is between about 250 Å and about 1000 Åthick. In one example, STI 225 is between about 1500 Å and about 2500 Åthick. In one example, BOX layer 210 is between about 1500 Å and about2500 Å thick. In one example, bonding layer 210 is between about 2500 Åand about 3500 Å thick. In one example, bonding layer 365 is betweenabout 2500 Å and about 3500 Å thick. In one example, etch stop layer 360is between about 250 Å and about 1000 Å thick.

Substrate 200 may be formed from an SOI substrate by removal of thesemiconductor (e.g., silicon) base layer under BOX layer 210 afterformation of FETs 240 followed by a deposition of a layer of LTO to formbonding layer 205 on BOX layer 225. Substrate 300 may be formed from anSOI substrate complete with ILD wiring set 330 followed by deposition ofetch stop layer 360 and a deposition of a layer of LTO to form bondinglayer 365.

In FIG. 2A, a photoresist layer 400 is formed on dielectric layer andpatterned to form an opening 405 in the photoresist layer in a mannersimilar to that described supra for opening 155 in photoresist 150 ofFIG. 1B. While no ARC (TARC or BARC) is illustrated in FIG. 2A, an ARC(TARC and/or BARC) may be used.

In FIG. 2B, an opening 410 is formed through dielectric layer 235,profile modulation layer 230, STI layer 225, BOX layer 210, bondinglayers 205 and 365 and etch stop layer 360 to expose a top surface ofwire 350. Then photoresist layer 400 (see FIG. 2A) is removed. Themethodology is similar to that described supra with respect to theformation of opening 155E of FIG. 1H. First dielectric layer 235 isRIE'd selective to profile modulation layer 230 using for example, amixed CO/C₄F₈/Ar gas derived plasma when dielectric layer 235 is siliconoxide and profile modulation layer 230 is silicon nitride. Thischemistry (at the proper bias, forward and reverse power, pressure andgas flows) etches silicon oxide about 25 times faster than siliconnitride. Second, profile modulation layer 230 is RIE'd selective todielectric layer 235 and STI 225, using, for example; a mixedCHF₃/CF₄/Ar gas derived plasma when dielectric layers 235 and STI 225are silicon dioxide and profile modulation layer is silicon nitride.This chemistry (at the proper bias, forward and reverse power, pressureand gas flows) etches silicon nitride about 4 times faster than siliconoxide. It is advantageous to keep profile modulation layer 230 (and etchstop layer 360) as thin as possible. Third, STI 235, BOX layer 210,bonding layers 205 and 365 are RIE'd selective profile modulation layer230 and etch stop layer 360 using, for example, a mixed CO/C₄F₈/Ar gasderived plasma when STI 235, BOX layer 210, bonding layers 205 and 365are silicon oxide and profile passivation layer 230 and etch stop layer360 are silicon nitride. The third RIE process is not selective todielectric layer 235 so opening 410 has a tapered profile in dielectriclayer 235, a substantially straight or slightly tapered profile in STI225, BOX 210, and bonding layers 205 and 365 (compared to the taper ofopening 410 in dielectric layer 235) because of the presence of profilemodulation layer 230. Fourth, photoresist layer 400 (see FIG. 2A) isremoved using an oxygen ash process. Fifth, etch stop layer 360 is RIE'dselective to dielectric layer 235. STI 225, BOX layer 210 and bondinglayers 205 and 365 using, for example, a mixed CF₄/CHF₃/Ar/O₂ gasderived plasma when etch stop layer 360 and profile modulation layer 230are silicon nitride and dielectric layer 210, STI 225, BOX layer 225 andbonding layers 205 and 365 are silicon oxide. Sixth an optional DC cleanusing N₂ and H₂ (i.e. a mixed N₂/H₂ gas derived plasma etch) isperformed.

In FIG. 2C, opening 410 (see FIG. 2B) is filled with an electricalconductor for an electrically conductive via 420 in electrical contactwith wire 350. In one example, via 420 is formed by deposition of anelectrically conductive liner on the sidewall of opening 410 (see FIG.2B) and top surface of dielectric layer 235 followed by overfilling theopening with an electrically conductive core conductor. In one example,the conductive liner comprises, in the order of deposition, a layer ofTaN, a layer of Ta and a layer of Cu and the core conductor compriseselectroplated copper. After filling the opening a CMP is performed toremove the liner and core conductor from over dielectric layer 235 toform the via 420 extending from a top surface 425 of dielectric layer235 to a top surface of wire 350. After the CMP, a top surface 430 ofvia 420 is coplanar with top surface 425 of dielectric layer 235. Thusvia 420 is a damascene via.

Electrically conductive contacts (not shown) may be made throughdielectric layer 235 to the S/Ds and gates of FETs 240. Alternatively,the contacts may be formed prior to formation of photoresist layer 400(see FIG. 2A). Additional interlevel dielectric layer containing wiresmay be formed on top of dielectric layer 235, the wires thereinelectrically connecting via 420 to FETs 240 and FETs 345 into circuits.See FIG. 34.

FIG. 3 is a cross-section of additional fabrication steps in thefabrication of three-dimensional integrated circuit according toembodiments of the present. In FIG. 3, an electrically conductivecontact 440 is formed to one of FETs 240 and an ILD wiring set 445 isformed on dielectric layer 235. ILD wiring level set 445 includes wires450 and a terminal pad 455. ILD wiring set 445 is illustrated having twoILD wiring levels. ILD wiring level set 445 may include more or less ILDlevels (down to one level containing wires/terminal pads 455) or as manylevels as required by the integrated circuit design. The ILD wiringlevels of ILD wiring set 445 are, by way of example, damascene anddual-damascene ILD levels formed by damascene and dual-damasceneprocesses. Contact 440 is illustrated as a damascene contact. One wire450 connects contact 440 to contact 420. Thus a three-dimensionalintegrated circuit is formed comprising FETs 240 and FETs 345. It shouldbe understood that ILD wiring level set may be formed over dielectriclayer 235 of FIG. 2C to generate a structure similar to that illustratedin FIG. 3, but where the upper substrate is a bulk silicon substrateinstead of an SOI substrate.

In both the examples of FIGS. 2A through 2C and 3, silicon layer 215 andBOX 210 is an SOI substrate and silicon layer 315 and BOX is an SOIsubstrate. It should be understood that substrate 300 may be replacedwith a bulk silicon substrate.

Thus the embodiments provide a process methodology for deep vias andsemiconductor devices using deep via structures that have profiles thatare less susceptible to metal fill problems.

The description of the embodiments of the present invention is givenabove for the understanding of the present invention. It will beunderstood that the invention is not limited to the particularembodiments described herein, but is capable of various modifications,rearrangements and substitutions as will now become apparent to thoseskilled in the art without departing from the scope of the invention.Therefore, it is intended that the following claims cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

1. A method, comprising: forming an etch stop layer on a top surface ofa substrate; forming a first dielectric layer on a top surface of saidetch stop layer; forming a profile modulation layer on a top surface ofsaid first dielectric layer; forming a second dielectric layer on a topsurface of said profile modulation layer; forming a photo-imaging layeron a top surface of said second dielectric layer; forming an opening insaid photo-imaging layer, a region of said top surface of said seconddielectric layer exposed in a bottom of said opening; reactive ionetching said second dielectric layer with a first etch chemistryselective to said profile modulation layer to form an opening throughsaid second dielectric layer; reactive ion etching said profilemodulation layer with a second etch chemistry selective to said firstand second dielectric layers to extend said opening through said profilemodulation layer; reactive ion etching said first dielectric layer witha third etch chemistry selective to said profile modulation layer andselective to said etch stop layer to extend said opening through saidfirst dielectric layer; reactive ion etching said etch stop layer with afourth etch chemistry selective to said first and second dielectriclayers to extend said opening through said etch stop layer; and removingsaid photo-imaging layer, after said removing said photo-imaging layer,said opening extending from said top surface of said second dielectriclayer, through said second dielectric layer, through said profilemodulation layer, through said first dielectric layer and through saidetch stop layer to said top surface of said substrate.
 2. The method ofclaim 1, wherein said third etch chemistry is not selective to saidsecond dielectric layer.
 3. The method of claim 1, wherein said firstand third etch chemistries are a same chemistry.
 4. The method of claim1, wherein said second and fourth etch chemistries are a same chemistry.5. The method of claim 1, wherein said removing said photo-imaging layeris performed between said reactive ion etching said first dielectriclayer and said reactive ion etching said etch stop layer.
 6. The methodof claim 1, wherein said first dielectric layer and second dielectriclayer comprise silicon oxide and said profile modulation layer and saidetch stop layer comprise silicon nitride.
 7. The method of claim 1,wherein: a first width of said opening measured in first directionparallel to said top surface of said second dielectric layer at said topsurface of said second dielectric layer is greater than a second widthof said opening measured in said first direction at said top surface ofsaid profile modulation layer and greater than a third width of saidopening measured in said first direction at said top surface of saidsubstrate, said second width greater than or equal to said third width;and wherein a ratio of a depth of said opening measured in a seconddirection perpendicular to said first direction from said top surface ofsaid second dielectric layer to said top surface of said substrate tosaid first width is equal to or greater than five.
 8. The method ofclaim 1, further including: after said removing said photo-imaginglayer, filling said opening with said electrical conductor.
 9. Themethod of claim 8, wherein said filling said opening with an electricalconductor comprises: depositing a tantalum nitride layer over sidewallsand a bottom of said opening; depositing a tantalum layer on saidtantalum nitride layer; depositing a seed copper layer said tantalumlayer; electroplating an electroplated copper layer on said seed copperlayer, said electroplated copper layer completely filling remainingspaces in said opening; and performing a chemical-mechanical-polish toremove said tantalum nitride layer, said tantalum layer, said seedcopper layer and said electroplated copper layer from over said topsurface of said second dielectric layer.
 10. The method of claim 1,wherein said photo-imaging layer includes a photoresist layer over anantireflective coating on said top surface of said first dielectriclayer and said forming said opening in said photo-imaging layercomprises exposing said photoresist layer to actinic radiation through apatterned photomask, developing said exposed photoresist layer andreactive ion etching said antireflective coating with an initial etchchemistry where said anti-reflective coating is not protected by saidphotoresist layer.
 11. The method of claim 10, wherein said initial etchchemistry is selective to said photoresist layer and said firstdielectric layer and wherein said initial, second and fourth etchchemistries are a same chemistry.
 12. A method, comprising: forming afirst substrate, said first substrate including: first transistorselectrically connected to a set of wiring levels, each wiring levelincluding electrically conductive wires in a respective dielectriclayer; an etch stop layer on a top surface of an uppermost wiring levelof said set of wiring levels that is furthest from said substrate, saidetch stop layer in contact with a wire of said uppermost wiring level;and a first dielectric bonding layer on a top surface of said etch stoplayer; forming a second substrate, said second substrate including: asecond dielectric bonding layer; a buried oxide layer on a top surfaceof said second dielectric bonding layer; a semiconductor layer on a topsurface of said buried oxide layer, said semiconductor layer includingsecond transistors electrically isolated from each other by dielectricisolation in said silicon layer; a profile modulation layer on a top ofsaid silicon layer and on a top surface of said dielectric isolation;and a first dielectric layer on a top surface of said profile modulationlayer; bonding a top surface of said first dielectric bonding layer to abottom surface of said second dielectric bonding layer, said first andsecond dielectric bonding layers, said buried oxide layer and saiddielectric isolation comprising a multilayer second dielectric layer;forming a photo-imaging layer on a top surface of said first dielectriclayer; forming an opening in said photo-imaging layer, a region of saidtop surface of said first dielectric layer exposed in a bottom of saidopening; reactive ion etching said first dielectric layer with a firstetch chemistry selective to said profile modulation layer to form anopening through said first dielectric layer; reactive ion etching saidprofile modulation layer with a second etch chemistry selective to saidfirst and second dielectric layers to extend said opening through saidprofile modulation layer; reactive ion etching said second dielectriclayer with a third etch chemistry selective to said profile modulationlayer and selective to said etch stop layer to extend said openingthrough said second dielectric layer; reactive ion etching said etchstop layer with a fourth etch chemistry selective to said first andsecond dielectric layers and to said wire to extend said opening throughsaid etch stop layer; removing said photo-imaging layer, after saidremoving said photo-imaging layer said opening extending from said topsurface of said first dielectric layer, through said profile modulationlayer, through said second dielectric layer, through said seconddielectric layer and through said etch stop layer to a top surface ofsaid wire; and filling said opening with an electrical conductor, saidelectrical conductor in electrical contact with said wire.
 13. Themethod of claim 12, wherein said third etch chemistry is not selectiveto said first dielectric layer.
 14. The method of claim 12, wherein saidfirst and third etch chemistries are a same chemistry.
 15. The method ofclaim 12, wherein said second and fourth etch chemistries are a samechemistry.
 16. The method of claim 12, wherein said removing saidphoto-imaging layer is performed between said reactive ion etching saidsecond dielectric layer and said reactive ion etching said etch stoplayer.
 17. The method of claim 12, wherein said first and seconddielectric bonding layers, said buried oxide layer and said first andsecond dielectric layers comprise silicon oxide and said profilemodulation layer and said etch stop layer comprise silicon nitride. 18.The method of claim 12, wherein: a first width of said opening measuredin first direction parallel to said top surface of said seconddielectric layer at said top surface of said second dielectric layer isgreater than a second width of said opening measured in said firstdirection at said top surface of said profile modulation layer andgreater than a third width of said opening measured in said firstdirection at a top surface of said substrate, said second width greaterthan or equal to said third width; and wherein a ratio of a depth ofsaid opening measured in a second direction perpendicular to said firstdirection from said top surface of said second dielectric layer to saidtop surface of said substrate to said first width is equal to or greaterthan five.
 19. The method of claim 12, wherein said filling said openingwith an electrical conductor comprises: depositing a tantalum nitridelayer over sidewalls and a bottom of said opening; depositing a tantalumlayer on said tantalum nitride layer; depositing a seed copper layersaid tantalum layer; electroplating an electroplated copper layer onsaid seed copper layer, said electroplated copper layer completelyfilling remaining spaces in said opening; and performing achemical-mechanical-polish to remove said tantalum nitride layer, saidtantalum layer, said seed copper layer and said electroplated copperlayer from over said top surface of said second dielectric layer. 20.The method of claim 12, wherein said photo-imaging layer includes aphotoresist layer over an antireflective coating on said top surface ofsaid first dielectric layer and said forming said opening in saidphoto-imaging layer comprises exposing said photoresist layer to actinicradiation through a patterned photomask, developing said exposedphotoresist layer and reactive ion etching said antireflective coatingwith an initial etch chemistry where said anti-reflective coating is notprotected by said photoresist layer.
 21. The method of claim 20, whereinsaid initial etch chemistry is selective to said photoresist layer andsaid first dielectric layer and wherein said initial, second and fourthetch chemistries are a same chemistry.
 22. The method of claim 12,further including: forming an electrically conductive contact throughsaid first dielectric layer to a transistor of said second transistorsof said second substrate; and forming an additional set of wiring levelson said top surface of said first dielectric layer, wires in saidadditional set of wires electrically connecting said electricalconductor in said opening to said contact through said first dielectriclayer.